-us -> -i is Latin, 2nd declension, masculine sg -> pl ; 2nd declension neuter is -um -> -i;

in Greek (and "pus" for "foot" is Greek, in 'octopus')...
We have Διόνυσος which some research online shows is almost certainly 2nd declension Greek, which pluralizes as Διόνυσοι or Dionysoi.